The results of a series of water droplet impingement erosion experiments on lead sulfide and zinc selenide are described. The work with single crystal lead sulfide sought to correlate the mechanisms of surface damage with mechanical strength, lead sulfide affording an opportunity to study the effect of a range of hardness, caused by a shift in stoichiometry into the p-type range, in specimens otherwise similar in elastic properties and pre-existing dislocation substructures. Dislocations involved in the deformation resulting from water droplet impacts were revealed by etch pitting. The size and nature of the impact sites on all the lead sulfide specimens studied, using 0.42 mm water droplets impacting at 100-168 m/s, was found to be in fact highly stochastic. The deformation produced was strongly dependent upon the pre-existing arrangement of dislocations at the imapct site, and considerable effort was expended in obtaining suitably dislocation-free crystal surfaces. The polycrystalline zinc selenide examined is a prime candidate material for windows for IR imaging devices. The grain boundaries in this material appeared to act as flaw sites which, upon repeated impact, led to the encirclement of complete grains by cracks, with consequent material loss.